Black Hole Formation in Fallback Supernova and the Spins of LIGO Sources

TL;DR

This study uses 3D hydrodynamical simulations to explore how fallback supernovae in binary systems influence the spins of black holes, revealing that initial binary separation significantly impacts the effective spin of LIGO-detected sources.

Contribution

It demonstrates that the effective spin of black holes formed in fallback supernovae is mainly affected by initial binary separation, challenging previous assumptions about formation pathways.

Findings

Black hole spin varies little with supernova energy.

Initial binary separation strongly influences the effective spin.

Formation pathways for LIGO sources may be more diverse than previously thought.

Abstract

Here we investigate within the context of field binary progenitors how the the spin of LIGO sources vary when the helium star-descendent black hole (BH) is formed in a failed supernova (SN) explosion rather than by direct collapse. To this end, we make use of 3d hydrodynamical simulations of fallback supernova in close binary systems with properties designed to emulate LIGO sources. By systematically varying the explosion energy and the binary properties, we are able to explore the effects that the companion has on redistributing the angular momentum of the system. We find that, unlike the mass, the spin of the newly formed BH varies only slightly with the currently theoretically unconstrained energy of the SN and is primarily determined by the initial binary separation. In contrast, variations in the initial binary separation yield sizable changes on the resultant effective spin of the system. This implies that the formation pathways of LIGO sources leading to a particular effective spin might be far less restrictive than the standard direct collapse scenario suggests.